CHARACTERIZATION OF THE PREVALENCE AND FECAL EGG COUNT INTENSITY OF GASTROINTESTINAL NEMATODES AND THEIR MANAGEMENT IN WESTERN CANADIAN COW-CALF HERDS

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Masters

Abstract

Gastrointestinal nematodes (GIN) have a negative impact on animal health and production in grazed beef cattle. The impact that GIN have on cattle is dependent on the interaction of many factors including the biology between the host (cattle) and the parasite, climate, cattle management/husbandry, pasture/stock management and varies between geographical locations, herd to herd and animal to animal. There is a scarcity of current information regarding GIN epidemiology and management specific to western Canadian beef cow-calf herds, an important sector of the agrarian economy. Therefore, the overarching objective of this thesis was to provide current information about the epidemiology and management of GIN in beef cow-calf herds of western Canada. This objective was examined in three parts: i) determining the prevalence and FEC intensity of gastrointestinal nematode burdens in different production types (cows, calves and replacement heifers), ii) characterizing the herd-level gastrointestinal nematode burden of heifers quantitatively and qualitatively by conducting fecal egg counts and determination of nematode larval species identity and iii) characterizing the current management strategies employed by producers in the control of gastrointestinal nematodes by producers of the western Canadian beef cow-calf industry. In study 1, fecal egg counts (FEC) provided by Merck Animal Health Canada from cows (n=1,780), calves (n=980) and replacement heifers (n=960) from 201 herds over 2012, 2013 and 2014 were analyze using generalized estimating equations (GEE) (STATA14) for the prevalence and mean eggs per gram (EPG) for Trichostrongylid-type eggs, Nematodirus spp. and Trichuris spp. The prevalence of Trichostrongylid-type eggs was uniformly high across all production types (78; 95% CI 75-82), while the mean EPG was consistently low (4.9; 95% CI 3.9-5.9). Nematodirus spp. egg positive samples came most frequently from calves, with an appreciably high predicted prevalence of 36% (95% CI 30-42). Trichuris spp. eggs were a very infrequent finding at an overall prevalence of 0.2% (7/3891; 95% CI 0.08 – 0.4). Study two used the same methodology as study 1. However, samples utilized were form 1,655 heifers (n=85 herds) enrolled in a pilot disease surveillance network (Western Canadian Cow-Calf Surveillance Network (WCCCSN)). The prevalence (95% CI) of Trichostrongylid-type egg positive samples was high at 92% (95% CI 89-95). The prevalence of Nematodirus spp. (2%; 95% CI 1-3) and Trichuris spp. (1%; 95% CI 1-2) was very low.
The level of FEC intensity was consistently low, with a mean EPG (95% CI) of Trichostrongylid-type eggs was 5.0 (95& CI 4.4– 5.9). Herds with >300 cow-calf pairs had a significantly (p<0.01) lower mean predicted Trichostrongylid-type EPG at 5.0 EPG (95% CI 3.6-6.5) compared to herds with ≤300 cow-calf pairs (5.3 EPG; 95% CI 4.4-6.2). For Study 3 in May 2016, 105 questionnaires were administered to producers enrolled in the WCCCSN pilot disease surveillance network described in study 2, to describe the current management strategies utilized by these herds to control GIN. Ninety-seven of the administered questionnaires were returned, for a response rate of 93%. The responses from the producers revealed the almost uniform dependence of producers on the use of a pour-on macrocyclic lactone parasite control product 96% (92/96; 95% CI 89-98) in the fall as part of a routine farm management program as the method of choice for the treatment of GIN in western Canadian beef cow-calf herds. The combined results of these studies reveal a high prevalence but low level of FEC intensity of GIN in western Canadian beef cow-calf herds across all animal production types. The results of the management questionnaire raise concerns about the impact that current management strategies may have on the development of anthelmintic resistance in GIN populations. This paired with the consistently high prevalence of GIN seen highlights the need for continuing research into the epidemiology, diagnosis and management of GIN in beef cow-calf herds of western Canada.